fn main() {
    // 卫语句 对match的值进行再过滤
    let pair = (2, -2);

    println!("{:?}", pair);
    match pair {
        (x, y) if x == y => println!("twins"),
        (x, y) if x + y == 0 => println!("两数之和==0"),
        (x, ..) if x % 2 == 1 => println!("odd"),
        _ => println!("xx"),
    }
}
